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JD65 20-Apr-2006 09:26 AM

bleeding brakes
 
I had to undo the brake line on the front master cylinder and now everthing is attached again i cant get the system to bleed. the master cylinder is pumping the fluid through to the calipers i have pumped a whole 500ml bottle through and still the lever is coming back to the bar. and i cant see any air coming out.

I also tried bleeding from the top banjo bolt but that did not help eather. any ideas. is there an air pocket in the top of the master cylinder?

Henners 20-Apr-2006 10:03 AM

I'm having the same problem but with the rear caliper on my 996 :(

All I would suggest is you can buy a banjo bolt for the joint next to the master cylinder on the clip-on with a built in bleed nipple which will make getting air trapped there out a piece of cake.

DaveO749R 20-Apr-2006 10:16 AM

Hi

I have experianced this a few times I suspected air trapped at the top of the banjo connection to the master cyclinder.

Try the following in this order.

1. Pump the brake lever a few times and tie wrap the lever back hard against the bar and leave it over night. Hopefully the air will move up and into your master cyclinder. If not move the bike into the sun and let the warm sun heat up master cyclinder hoping the trapped air inside expands and then moves up into the cyclinder. Sounds daft but it works.

2. Use a syringe (cost coppers from a local store) attach the bleed hose to the end fill it with fresh fluid connect it to your caliper bleed nipple and force the fluid up through the system into your master cyclinder. Use a reasonable sized syringe to ensure enough fluid is pushed through the system ensuring no air remains (oh and don't forget to keep and eye on the expansion bottle as the fluid comes up empty it with a second syringe).

Just keep trying u will get there in the end.

Regards

Dave O

DaveO749R 20-Apr-2006 10:19 AM

Henners

If its an under slung rear caliper they are a pain to bleed u need to lift it higher than the master cyclinder (ask the wife to hold it she'll luv that not lol).

Then bleed in the normal way with a non return valve its so easy then, when the air stops refit and it will be A OK.


Regards

DaveO

andyb 20-Apr-2006 12:01 PM

Quote:

Originally posted by DaveO749R
Hi

I have experianced this a few times I suspected air trapped at the top of the banjo connection to the master cyclinder.

Try the following in this order.

1. Pump the brake lever a few times and tie wrap the lever back hard against the bar and leave it over night. Hopefully the air will move up and into your master cyclinder. If not move the bike into the sun and let the warm sun heat up master cyclinder hoping the trapped air inside expands and then moves up into the cyclinder. Sounds daft but it works.

2. Use a syringe (cost coppers from a local store) attach the bleed hose to the end fill it with fresh fluid connect it to your caliper bleed nipple and force the fluid up through the system into your master cyclinder. Use a reasonable sized syringe to ensure enough fluid is pushed through the system ensuring no air remains (oh and don't forget to keep and eye on the expansion bottle as the fluid comes up empty it with a second syringe).

Just keep trying u will get there in the end.

Regards

Dave O

I would challenge the use of "forcing fluid in with a syringe as it would inevitably have air in it.

However, i would use a syring to draw the fluid through by attatching it to the bleed pipe. This does work and will draw out the air as well as you new clean fluid. With the undrslung rear calliper, you do need to unbolt it and mount it on top of the disc to bleed!

Wylie1 20-Apr-2006 12:51 PM

I had a similar problem after replacing the fluid in my clutch (air at/around lever). Initially, it was fine, but then the lever started coming further & further back to the bar.

There is a bleed valve in the reservoir itself (on the clutch side anyway!). Assuming there's one in the front brake reservoir as well, take cover off, then squeeze lever as you undo valve. Tighten valve as the lever gets close to the bar. Only took 3 squeezes & the clutch was perfect!

moto748 20-Apr-2006 01:09 PM

I seldom have a problem bleeding my brakes, thanks to my trusty Mityvac (and I know some people think they're a waste of money; you can do it just as easy with syringe, whatever, but what swayed it for me is: the professionals use them), bur came across a new prob the other day~: sheared the bloody bleed nipple off (the brake master cylinder one). This was undoing it too, so I can't say I was doing it up too tight.

Now that'll hasve to wait until I can get louigi to have a go at drilling it out for me. Or it might be as cheap/easy to fit a second-hand m/cylinder.

Jools 20-Apr-2006 01:33 PM

I think that folks are on the right lines. I just replaced the entire front brake system on my 888 with new billet callipers, new stainless lines and a 'new' master cylinder from an ST4S, so basically the whole system was full of air.

The master cylinder was pumping fluid through to the calipers, but not very effectively, and as you say the lever was coming back to the bar. So I had to bleed it at the master cylinder banjo end. I'm running twin lines from the master cylinder so there were two banjo bolts, a spacer and 4 copper washers in total, seperating the joints. There were plenty of joints for fluid to seep out from, so it can be a messy business and you'll need loads of highly absorbant rag underneath the master banjo. Then, just crack the banjo open and squeeze the lever slowly - don't squeeze it fast otherwise the fluid can spit out from between each joint (even if you only have a single line with two joints to worry about) and spray everywhere - don't ask me how I know. Hold the lever right back to the bar for a couple of seconds, then tighten the banjo up. Do this a few times until you're sure that there is just fluid seeping out of the cracks between the banjo(s), it may take more goes than you'd think.

It might help if you have a bottle of muc-off or similar and a hose handy as well. Once I had made sure that there was no air in the master, and put the master cylinder cap back on to make sure I didn't get water in the master reservoir I gave the whole area a good squirt of cleaner and rinsed it all down to make sure that I didn't have unseen splashes of brake fluid hanging around on my paintwork.

Once the master was bled through, I went back to bleeding the callipers as normal until I got a good lever feel, then I squeezed the lever back hard and cable tied it to the bar overnight. I went out the next day for a 200+ mile rideout and the brakes were fine all day although the lever was still a bit soft for my liking.

I think I will repeat the process again this weekend, and as often as necessary to get every last gasp of air out of the system. The other thing that might have affected mine was that I bought a fresh bottle of brake fluid before I started and filled the reservoir up once. I sat the bottle a good few feet away from the bike because I'm paranoid about brake fluid getting spilled, but sods law dictated that while I was busy bleeding the master cylinder the bottle fell over and emptied itself completely over my path. So, I had to finish bleeding the system with a bottle of fluid that's been sitting around half full for a couple of months, this may have absorbed a bit more water than ideal, so the system may need flushing through with fresh fluid before it's perfect.

JD65 20-Apr-2006 01:43 PM

thanks guys i'll keep trying

phoenix n max 20-Apr-2006 02:22 PM

Always do mine by sucking it out with a syringe thesedays after a fruitless 2 hours trying to bleed them when i fitted a twin disc conversion.

Never have any problems now.


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